<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>span标签</title>

    <style>
        #userSpan{
            color:#999;
            font-size: 12px;
        }


    </style>


</head>
<body>
    <span>这是一个非常干净的标签</span>
    <br>

    用户名:<input type="text"><span id="userSpan">*用户的格式</span>
</body>
</html>